This is something I'm devising for a conworld. Right now I'm contemplating a religion that, like Islam, insists on preserving the original version of their holy book. But simply preserving it isn't enough, they want the original text to remain be intelligible for eternity.
Part of this has to do with their view on art: they hate it and view it as sorcery. And just so we know, no, the religion isn't really based off of Islam (much), but it is inspired by the Abrahamic family in general. In a way it looks like a long-lost member of that family. Anyway, like I said, they hate art. In general they're extremely anti-materialist and think art is at best a useless distraction, at worst a form of mind-controlling sorcery. In the case of their holy book, they want people to pay attention solely to what the text says, rather than how pretty it sounds. The founder of the religion himself advocated this, and the entire text is written in a very boring, almost robotic fashion. Thinking about the grammar, it actually bears a mild resemblance to Lojban.
Thinking about it, there are ways they can keep the text intelligible despite language changing over time. Like some modern real-world languages, the spelling system may be slower to change than the spoken language, resulting in a lot of spelling irregularities, but keeping older texts intelligible for longer. But this would probably only work for a few centuries. Another way would be for the book to be written with a logographic system, allowing pronunciation to change freely but the text still being intelligible as long as the grammar remains the same. But I find it hard to believe that the religion's founder would have that much sense. I'm not sure how old the religion is, I'm thinking between 1500 and 3000 years old. I'm kind of leaning towards a younger date though, because I like to think that they actually keep the original book written by the very hand of their founder, and I highly doubt a book or scroll could last for thousands of years, no matter how much you do to preserve it.
But really thinking about it, they probably wouldn't bother to write any books besides copies of their holy book and maybe their own history. Honestly, I doubt they would even have a word for 'book', when the only book most people know of is their own holy book. I like to think the name of the book is simply translated as 'the book'. Foreigners simply choose to use the name of their holy book because they simply had no other word for book.
And yes, they're anti-materialist to an impractical extreme. They almost look like Jains. Really the only possessions they see as okay to possess is clothing, shelter, and food. And the average person doesn't make use of much more than that. They keep copies of their holy book, of course, they also use a tool for both chopping and hoeing the soil for their crops (the thing looks like an Adze, if you care), a clay pot to boil their food in, and a simple loom to make cloth. These people don't even know how to work metal (they just 'slot' boards together to make buildings, like the real-world Japanese used to do, rather than use nails). They don't make use of wagons, or wheels. Think of the Amish, except they essentially only use stone-age technology. Note that I'm still working out what kinds of tools they make. I know they would need knives (they do eat meat, and they make their clothing out of wool so they would need something to shear sheep), and I don't know if an Adze would have the precision they need to make their houses. Not sure how they could make a saw without metal-working though. I guess they could use stone chisels...